Some medicines have a very short shelf-life unless kept refrigerated. For example, TPA, used in treating heart attacks, must be kept under refrigeration when in its liquid form.
One way to extend the room temperature shelf-life of some medicines is by removing the liquid from the medicine and storing the medicine in a dry form. When the medicine is to be used, liquid, typically sterile water, is added to the dry medicine to reconstitute the medicine to its liquid form. If the medicine is to be taken orally, the thoroughness of mixing is generally not a great problem. However, many medicines are injected into the user. In these cases, the mixing must be especially thorough and complete.
Hydrating syringes have been developed to store the dry and liquid components of the medicine in separate compartments. The compartments are fluidly connected, the contents are mixed together and then the mixture is injected into the patient. One of the problems with these prior art hydrating syringes is that incomplete mixing often occurs leaving a residue of the dry component in the syringe. Incomplete mixing of the dry and liquid components of the medicine may be caused at least in part when mixing is restricted to one pass of the liquid component into the region of the syringe containing the solid component. Thus, existing hydrating syringes are not as efficient or effective as may be desired.